ABSTRACT
Transdermal dosage forms provide controlled drug dosing through the skin from bandage-like delivery systems. This method of drug delivery can provide certain medical advantages for many drugs. The skin is a very good barrier preventing the absorption of such foreign substances; therefore, most drugs don’t diffuse through it rapidly enough for ordinary formulations to be administered transdermally. Skin permeation enhancers increase skin permeability and may make it feasible to deliver many more drugs transdermally. In addition, they may be useful for improving the efficacy of poorly permeating, topically acting drugs. The literature on skin permeation enhancers is reviewed, with particular emphasis on structure/activity relationships, mechanisms of enhancing skin permeability, and toxicity of skin permeation enhancing agents. Although this summary may not enable one to predict how to effectively and safely enhance transdermal or dermal delivery for some given drug, it should provide an understanding of the studies that are important to reaching such a target. As an introduction, the properties of skin as a barrier and the pathways of transport across the skin are discussed.
